Gaseous fuel powered engines are common in locomotive applications. For example, the engines of a locomotive can be powered by natural gas. A preferred form of natural gas for transport with locomotives is liquefied natural gas (LNG) because of its higher energy density. The LNG can be transported in a tender car, pressurized, and heated into a gaseous state before it is delivered to a locomotive engine. The compressed natural gas (CNG) may be injected into the cylinders of the engine and ignited, such as by a spark or pilot fuel (e.g., diesel fuel). In one example, CNG is injected using high pressure direct injection (HPDI), where a high pressure pump pressurizes LNG before it is warmed to a supercritical gaseous state and then sent to an HPDI injector.
An example of a gaseous fuel powered locomotive is disclosed in PCT Application WO 2013/091109 by Melanson et al., published Jun. 27, 2013 (“the '109 reference”). The '109 reference discloses a system for supplying gaseous fuel from a tender car to an internal combustion engine on a locomotive. The system includes a fuel pump that delivers fuel from the tender car tank to an engine on the locomotive for consumption. The liquefied fuel is gasified through heating prior to reaching the engine. A. controller communicates with a pressure sensor and the fuel pump to maintain a pressure of gaseous fuel in the delivery conduit at a near-constant level.
While the system of the '109 reference may allow liquefied fuel to be transported and converted to gaseous fuel for an engine, it and other similar fuel systems may suffer from certain drawbacks. In particular, fuel systems that utilize a tender car for transporting liquefied fuel (e.g., LNG), such as the system of the '109 reference, require well-insulated fuel conduits to transfer the fuel from the tender car tank, through the various pumps, and to the engine. However, even with significant insulation, fuel inside these fuel conduits may experience a change in state or pressure, such as while the fuel system is not in operation. In one example, liquefied fuel that remains in a fuel conduit and/or pump after operation of the fuel system may warm to vapor conditions (e.g., due to outside temperatures, a prolonged period of non-use, etc.), causing the pump (e.g., a high-pressure pump) to lose prime. The pump cannot be primed (and, thus, operate properly) until the vaporized fuel is purged from the system. Fuel pressure cannot be controlled without the pump first being primed.
One solution for priming the pump is sending liquefied fuel to the pump while redirecting the vaporized fuel back to the tender car tank. This solution is less than ideal, however, because it requires additional plumbing and valves, increasing costs and complexity of the system. In addition, adding the vaporized fuels to the reservoir in the tank raises the temperature of the tank and subsequently increases the risk of fuel being vented out of the tank, thus wasting fuel and polluting the environment.
The disclosed fuel system is directed to overcoming one or more of the problems set forth above and/or other problems with existing technologies.